Foundations and Applications

HYDROGEN

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Overview

Hydrogen is the most abundant element in the universe. Nearly nine out of
every ten atoms in the universe are hydrogen atoms. Hydrogen is also
common on the Earth. It is the third most abundant element after
oxygen
and
silicon.
About 15 percent of all the atoms found on the Earth are hydrogen atoms.

Hydrogen is also the simplest of all elements. Its atoms consist (usually)
of one proton and one electron.

Hydrogen was first discovered in 1766 by English chemist and physicist
Henry Cavendish (1731-1810). Cavendish was also the first person to prove
that water is a compound of hydrogen and oxygen.

Discovery and naming

Hydrogen was probably "discovered" many times. Many early
chemists reported finding a "flammable gas" in some of their
experiments. In 1671, for example, English chemist Robert Boyle (1627-91)
described experiments in which he added iron to hydrochloric acid (HCl)
and sulfuric acid (H
2
SO
4
). In both cases, a gas that burned easily with a pale blue flame was
produced.

The problem with these early discoveries was that chemists did not
understand the nature of gases very well. They had not learned that there
are many kinds of gases. They thought that all the "gases"
they saw were some form of air with impurities in it.

Cavendish discovered hydrogen in experiments like those that Boyle
performed. He added iron metal to different acids and found that a
flammable gas was produced. But Cavendish thought the flammable gas came
from the iron and not from the acid. Chemists later showed that iron is an
element and does not contain hydrogen or anything else. Therefore, the
hydrogen in Cavendish's experiment came from the acid:

Hydrogen was named by French chemist Antoine-Laurent Lavoisier (1743-94).
Lavoisier is sometimes called the father of modern chemistry because of
his many contributions to the science. Lavoisier suggested the name
hydrogen after the Greek word for "water former" (that which
forms water). (See sidebar on Lavoisier in the
oxygen
entry in volume 2.)

Physical properties

Hydrogen is a colorless, odorless, tasteless gas. Its density is the
lowest of any chemical element, 0.08999 grams per liter. By comparison, a
liter of air weighs 1.29 grams, 14 times as much as a liter of hydrogen.

Hydrogen changes from a gas to a liquid at a temperature of -252.77°C
(-422.99°F) and from a liquid to a solid at a temperature of
-259.2°C (-434.6°F). It is slightly soluble in water, alcohol,
and a few other common liquids.

Chemical properties

Hydrogen burns in air or oxygen to produce water:

Stars use hydrogen as a fuel with which to produce energy.
Antares—the brightest star in the constellation
Scorpius—is shown here.

It also combines readily with other non-metals, such as
sulfur, phosphorus,
and the halogens. The halogens are the elements that make up Group 17
(VIIA) of the periodic table. They include
fluorine, chlorine, bromine, iodine,
and
astatine.
As an example:

Occurrence in nature

Hydrogen occurs throughout the universe in two forms. First, it occurs in
stars. Stars use hydrogen as a fuel with which to produce energy. The
process by which stars use hydrogen is known as fusion. Fusion is the
process by which two or more small atoms are pushed together to make one
large atom. In most stars, the primary fusion reaction that occurs is:

This equation shows that four hydrogen atoms are squeezed together (fused)
to make one helium atom. In this process,
enormous amounts of energy are released in the form of heat and light.

Hydrogen also occurs in the "empty" spaces between stars. At
one time, scientists thought that this space was really empty, that it
contained no atoms of any kind. But, in fact, this interstellar space
(space between stars) contains a small number of atoms, most of which are
hydrogen atoms. A cubic mile of interstellar space usually contains no
more than a handful of hydrogen and other atoms.

Hydrogen occurs on the Earth primarily in the form of water. Every
molecule of water (H
2
O) contains two hydrogen atoms and one oxygen atom. Hydrogen is also found
in many rocks and minerals. Its abundance is estimated to be about 1,500
parts per million. That makes hydrogen the tenth most abundant element in
the Earth's crust.

Hydrogen also occurs to a very small extent in the Earth's
atmosphere. Its abundance there is estimated to be about0.000055 percent.
Hydrogen is not abundant in the atmosphere because it has such a low
density. The Earth's gravity is not able to hold on to hydrogen
atoms very well. They float away into outer space very easily. Most of the
hydrogen that was once in the atmosphere has now escaped into outer space.

Isotopes

There are three isotopes of hydrogen, hydrogen-1, hydrogen-2, and
hydrogen-3. Isotopes are two or more forms of an element. Isotopes differ
from each other according to their mass number. The number written to the
right of the element's name is the mass number. The mass number
represents the number of protons plus neutrons in the nucleus of an atom
of the element. The number of protons determines the element, but the
number of neutrons in the atom of any one element can vary. Each variation
is an isotope.

The three isotopes of hydrogen have special names. Hydrogen-1 is sometimes
called protium. It is the simplest and most common form of hydrogen.
Protium atoms all contain one proton and one electron. About 99.9844
percent of the hydrogen in nature is protium.

The man who gave hydrogen its name, Antoine-Laurent Lavoisier, is
sometimes called the father of modern chemistry.

Hydrogen-2 is known as deuterium. A deuterium atom contains one proton,
one electron, and one neutron. About 0.0156 percent of the hydrogen in
nature is deuterium.

The third isotope of hydrogen, hydrogen-3, is tritium. An atom of tritium
contains one proton, one electron, and two neutrons. There are only very
small traces of tritium in nature.

Tritium is a radioactive isotope. A radioactive isotope is one that breaks
apart and gives off some form of radiation. Some radioactive isotopes
(such as tritium) occur in nature. They can also be produced in the
laboratory. Very small particles are fired at atoms. These particles stick
in the atoms and make them radioactive. Tritium is a widely used isotope
and is now made in large amounts in the laboratory.

Tritium is widely used as a tracer in both industry and research. A tracer
is a radioactive isotope whose presence in a system can easily be
detected. The isotope is injected into the system at some point. Inside
the system, the isotope gives off radiation. That radiation can be
followed by means of detectors placed around the system.

Tritium is popular as a tracer because hydrogen occurs in so many
different compounds. For example, suppose a scientist wants to trace the
movement of water through soil. The scientist can make up a sample of
water made with tritium instead of protium. As that water moves through
the soil, its path can be followed by means of the radioactivity the
tritium gives off.

Tritium is also used in the manufacture of fusion bombs. A fusion bomb is
also known as a hydrogen bomb. In a fusion bomb, small atoms are squeezed
together (fused) to make a larger atom. In the process, enormous amounts
of energy are given off. For example, the first fusion bomb tested by the
United States in 1952 had the explosive power of 15 million tons of TNT. A
type of fusion bomb fuses tritium with deuterium to make helium atoms:

Stars use hydrogen as a fuel with which to produce energy.

Extraction

The obvious source for hydrogen is water. The Earth has enough water to
supply people's need for hydrogen. The problem is that it takes a
lot of energy to split a water molecule:

In fact, it simply costs too much to make hydrogen by this method. The
cost of electricity is too high. So it is not economical to make hydrogen
by splitting water.

A number of other methods can be used to produce hydrogen, however. For
example, steam can be passed over hot charcoal (nearly pure
carbon):

The same reaction can be used with steam and other carbon compounds. For
example, using methane, or natural gas (CH
4
), the reaction is:

Hydrogen can also be made by the reaction between carbon monoxide (CO) and
steam:

Because hydrogen is such an important element, many other methods for
producing it have been invented. However, the preceding methods are the
least expensive.

Uses

The most important single use of hydrogen is in the manufacture of ammonia
(NH
3
). Ammonia is made by combining hydrogen and nitrogen at high pressure and
temperature in the presence of a catalyst. A catalyst is a substance used
to speed up or slow down a chemical reaction. The catalyst does not
undergo any change during the reaction:

Ammonia is a very important compound. It is used in making many products,
the most important of which is fertilizer.

Hydrogen is also used for a number of similar reactions. For example, it
can be combined with carbon monoxide to make methanol—methyl
alcohol, or wood alcohol (CH
3
OH):

Tritium (hydrogen-3, the third isotope of hydrogen), is used in the
manufacture of fusion bombs.

Like ammonia, methanol has a great many practical uses in a variety of
industries. The most important use of methanol is in the manufacture of
other chemicals, such as those from which
plastics are made. Small amounts are used as additives to gasoline to
reduce the amount of pollution released to the environment. Methanol is
also used widely as a solvent (to dissolve other materials) in industry.

Another important use of hydrogen is in the production of pure metals.
Hydrogen gas is passed over a hot metal oxide to produce the pure metal.
For example,
molybdenum
can be prepared by passing hydrogen over hot molybdenum oxide:

The
Hindenburg
explosion

T
he
Hindenburg
was Germany's largest passenger airship. It was built in 1936 as
a luxury liner, and made the trip to the United States faster than an
ocean liner.

The
Hindenburg
was designed to be filled with helium, a safer gas than the highly
flammable hydrogen. But in those post-World War II days, the United
States suspected that Germany's new leader, Adolf Hitler
(1889-1945), had military plans for helium-filled ships. So the United
States refused to sell helium to the Zeppelin air-ship company. Seven
million cubic feet of hydrogen was used instead. This made the crew very
nervous about the potential for fire. Passengers were even checked for
matches as they boarded!

On May 3, 1937, the
Hindenburg
left Frankfurt, Germany, for Lakehurst, New Jersey. It travelled over
the Netherlands, down the English Channel, through Canada, and into the
United States. Bad weather forced the ship to slow down several times,
lengthening the trip. But it finally approached the field in Lakehurst
around 7:00 P.M. on May 6.

After several minutes of maneuvers due to rain and wind, crewmen dropped
ropes to the ground at 7:21. The ship was 200 feet above ground. Four
minutes later, a small flame emerged on the skin of the ship, and
crewmen heard a pop and felt a shudder. Seconds later, the
Hindenburg
exploded. Flaming hydrogen blasted out of the top. Within 32 seconds,
the entire airship had burned, the framework had collapsed, and the
entire ship lay smoldering on the ground. Thirty-six people died.
Amazingly, 62 survived.

Although claims of sabotage have always surrounded the
Hindenburg
tragedy, American and German investigators both agreed it was an
accident. Both sides concluded that the airship's hydrogen was
ignited probably by some type of atmospheric electric discharge.
Witnesses had noticed some of the skin of the ship flapping; they also
observed the nose of the ship rise suddenly. Both indicate the
likelihood that free hydrogen had escaped. The
Hindenburg
disaster ended lighter-than-air air-ship travel for many decades.

Hydrogenation is an important procedure to the food industry. In
hydrogenation, hydrogen is chemically added to another

The dramatic explosion of the
Hindenburg
in 1937 occurred when hydrogen was ignited.

substance. The reaction between carbon monoxide and hydrogen is an
example of hydrogenation. Liquid oils are often hydrogenated.
Hydrogenation changes the liquid oil to a solid fat. Most kitchens contain
foods with hydrogenated or partially hydrogenated oils. Vegetable
shortening, such as Crisco, is a good example. Hydrogenation makes it
easier to pack and transport oils.

Hydrogen is also used in oxyhydrogen ("oxygen + hydrogen")
and atomic hydrogen torches. These torches produce temperatures of a few
thousand degrees. At these temperatures, it is possible to cut through
steel and most other metals. These torches can also be used to weld (join
together with heat) two metals.

Another use for hydrogen is in Lighter-than-air balloons. Hydrogen is the
least dense of all gases. So a balloon filled with hydrogen can lift very
large loads. Such balloons are not used to carry people. The danger of
fire or explosion is too
great. On May 6, 1937, a hydrogen fire destroyed the German airship
Hindenburg,
as it was landing in Lakehurst, New Jersey; 36 people died. Today,
hydrogen balloons are used for lifting weather instruments into the upper
atmosphere.

One of the best known uses of hydrogen is as a rocket fuel. Many rockets
obtain the power they need for lift-off by burning oxygen and hydrogen in
a closed tank. The energy produced by this reaction provides thrust to the
rocket.

Solving the world's energy problems

M
ost people don't worry about filling their cars with gas. They
seem to believe that there will always be enough coal, oil, and natural
gas to keep civilization running. Those three fuels—the
"fossil fuels"—are what keep people on the move
today. They fuel cars and trucks, heat homes and offices, and keep
factories operating.

But fossil fuels will not last forever. At some point, all the coal,
oil, and natural gas will be gone. What source of energy will humans
turn to?

Some people believe that hydrogen is the answer. They talk about the day
when the age of fossil fuels will be replaced by a hydrogen economy.

"Hydrogen economy" refers to a world in which the burning
of hydrogen will be the main source of energy and power. Hydrogen seems
to be a good choice for future energy needs. When it burns, it produces
only water:

A lot of energy is produced in this reaction. That energy can be used to
operate cars, trucks, trains, boats, and airplanes. It can be used as a
source of heat for keeping people warm and running chemical reactions.

Why doesn't a hydrogen economy exist today? The answer is easy.
It is still too expensive to make hydrogen gas. No one has found a way
to remove hydrogen from water or some other source at a low cost. It is
still cheaper to mine for coal or drill for oil than to make hydrogen.

But that may not always be true. Some day, someone will find a way to
make hydrogen cheaply. When that happens, the day of the hydrogen
economy will have arrived.

Health effects

Hydrogen is essential to every plant and animal. Nearly every compound in
a living cell contains hydrogen. It is harmless to humans unless taken in
very large amounts. In this case, it is dangerous only because it cuts off
the supply of oxygen humans need to breathe.

I'm currently working on concepts for building a hydrogen plant for my company. I'm having trouble with getting the tritium and protium to actually collide to force the fusion in a controlled environment cost effectively. Any insight would be extremely helpful and could save me valuable resources and time.

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